Sexy corset-clad Rihanna gives thousands of fans a scare by COLLAPSING while belting out her mega-hit Umbrella.

The 20-year-old launched into the song to close a sizzling concert performance, but suddenly clutched her stomach and hunched over.

Internet footage shows her unable to continue and hurriedly lurching off stage. Seconds later she fell gasping into a chair, leaving boyfriend and music partner Chris Brown to end the gig.

A hospital check showed she'd been dehydrated because the venue in Sydney, Australia, on Friday was too hot. Barbados-born Rihanna, whose other hits include Disturbia and Live Your Life, had been carried around the arena on a harness. Her spokesman said: "It was very hot. She needed to sit, catch her breath and have some water."